The present invention relates generally to an apparatus for depositing multilayer coatings onto sheet substrates and devices mounted thereon, and more particularly to an encapsulation tool that performs multilayer coating processing while simultaneously reducing the likelihood of individual layer contamination.
Multilayer coatings have been included in the packaging for environmentally sensitive products and devices to protect them from permeation of environmental gases or liquids, such as oxygen and water vapor in the atmosphere, or chemicals used in product or device processing, handling, storage, or use. In one form, these coatings may be made from layers of an inorganic metal or metal oxide separated by layers of an organic polymer. Such coatings have been described in, for example, U.S. Pat. Nos. 6,268,695, 6,413,645 and 6,522,067, and allowed U.S. patent application Ser. No. 09/889,605, all incorporated herein by reference. One method commonly used to apply thin multilayer coatings to various web substrates is the “roll-to-roll” method, which involves mounting the continuous web substrate on a reel. A series of rotating drums are used to convey the substrate past one or more deposition stations. As the web passes around the drums in the system, polymer layers are deposited and cured at one or more polymer deposition and curing stations, while inorganic layers are deposited at one or more inorganic layer deposition stations. The deposition and curing stations are not separate chambers coupled together, but rather are adjacently spaced relative to one another within a single vacuum chamber. With such an open architecture, efforts must typically be made to minimize migration of the organic vapor which could otherwise lead to layer or substrate contamination. In addition, since vapor deposition imparts a significant heat load to the receiving substrate, one or more of the drums can be configured to provide a needed heat sink to control substrate temperature. While the roll-to-roll method is capable of high production rates, its practical use is limited to substrates that are continuous lengths (rolls). In addition, the flexure inherent in the roll-to-roll approach makes it difficult to deposit coatings onto rigid substrates or to substrates supporting inflexible devices mounted thereto.
When the substrate to be coated is in the form of discrete sheets, rather than a continuous web, another method, called the “cluster tool” method, is commonly used to apply the multilayer coatings to the sheet substrate. The cluster tool method, which is commonly used in the manufacture of semiconductor devices, involves the use of two or more independent vacuum chambers connected together via common interface, where each vacuum chamber contains one or more deposition sources. In the cluster tool approach, discrete sheet substrates are moved from one vacuum chamber to another to accept the different layers thereon, with the process being repeated as many times as necessary to produce the desired built-up coating. One of the strong motivators for developing the cluster tool approach was the need to isolate potential contamination sources between adjacent yet disparate layers, where typically isolation valves are placed between adjacent chambers. In fact, the use of cluster tool-based machinery for the barrier coating industry was based in part on the perception that organic and inorganic deposition could not take place within a common vacuum chamber if contamination was to be avoided. Another attribute of the cluster tool approach is that the potential for precise temperature control of the substrate is greater within each discrete vacuum chamber than it is for the open chambers of the roll-to-roll configuration. While the cluster tool approach has the benefit of producing relatively contaminant-free finished products, the constant exchange of the sheet substrate from one isolated vacuum chamber to another while maintaining a vacuum adds considerable complexity to design and control systems.
Accordingly, there is a need for a tool that can apply multilayer coatings to a sheet substrate and devices or products mounted on a sheet substrate that combines the speed and efficiency of roll-to-roll devices with the ability to prevent cross contamination inherent in cluster tool-based machines.